Traditionally, particulate detergent compositions have been manufactured by the spray drying process, in which a slurry of components such as anionic detergent active, builder material and optionally non-anionic detergent active is manufactured and then dried by atomising it and spraying it into a stream of air at high temperature. The spray-dried compositions are found in practice to have bulk densities less than 600 g/l. There are limits on the quantity of anionic detergent active that can be included due to the need to form a slurry before spray-drying. The resultant spray-dried granules may be used directly as a detergent composition or other components may be post-dosed, for example heat or moisture sensitive components, to provide a complete powder composition.
In recent years, a number of detergent powder manufacturing processes have been developed in which a spray-drying tower is not used. Such so called non-tower route (NTR) processes typically involve granulation of anionic detergent active and builder in a high or medium speed mixer/densifier, typically in the presence of a liquid binder such as water or non-anionic detergent active. High detergent active compositions having medium to high bulk densities (500-900 g/l) have been produced by such non-tower processes.
However, it has been found that such so called concentrated products may have unsatisfactory dispensing properties in wash water, particularly in automatic washing machines. Problems have been encountered such as poor dispersion of the powder into the wash water in the dispenser drawer of a washing machine. A gritty, viscous mass may remain in the dispenser drawer. Further, powder compositions entrained in the wash water may not break up and disperse adequately. Undissolved particles of powder compositions may remain in the wash water. These can adhere to clothes and cause local damage. For example, where the detergent composition contains bleach, an undissolved mass of composition can adhere to clothing and, due to the locally high concentration of bleach, damage the clothing. Undissolved powder composition can remain on the clothes after washing.